Diesel internal combustion engines produce and emit into the atmosphere exhaust streams containing various combustion byproducts. These exhaust streams may pollute and negatively impact the environment. Such exhaust streams may contain nitric oxides (NOx), for example, which contribute to smog and acid rain. Such exhaust streams may also contain particulate matter (PM).
To reduce NOx emission levels, diesel internal combustion engines may be paired with Selective Catalytic Reduction (SCR) treatment systems. In general, an automotive grade DEF, such as a urea-based DEF solution, is injected into the exhaust stream upstream of a SCR catalyst. The urea decomposes and hydrolyzes to form ammonia (NH3) which, in the presence of the SCR catalyst, reacts with the NOx in the exhaust stream and converts it into nitrogen, water, and small amounts of carbon dioxide (CO2), all natural components of air.
SCR systems may use an injector assembly or nozzle to inject the DEF into the exhaust stream. The injected DEF should evaporate and be thoroughly mixed with the exhaust stream. However, in practice, some of the injected DEF may form unwanted crystals in and around the exhaust outlet of the injector assembly or surrounding structures, which may lead to clogging of the injector assembly and insufficient mixing with the exhaust stream.